I have been roasting on Ambex YM2 for several years now, and have really enjoyed the coffee produced. I recently purchased a IKAWA PRO100 and have enjoyed the capability of experimenting with various roast profiles. One difference I have noticed with the IKAWA is the bloom. Even coffee just roasted does not bloom nearly as much as the coffee roasted on the Ambex. Not that it is big issue, the coffee roasted on the IKAWA has plenty of flavor, just trying to understand what is causing this to happen.

Are the beans swollen?

Some say that it is conduction - or lack thereof, in the air roaster case. I have no idea if this is true.

All I know is those Japanese shop roasters that have no forced airflow produce roasts with huge blooms in pour over.

Beans are not swollen, They appear the same between the roasting methods.

I've made small adjustments in my Ikawa's roast profile (with the same greens) that produced a significant change in the amount of crema when pulling a shot. Granted, how I pull the shot has a lot more to do with it, but I have observed a link to the roast profile. So, it could be a fluid-bed thing, but it could also be a roast profile thing.

Length of roast? Only way to have meaningful thoughts on the matter is to see graphs. There was a thread a while ago where a member named Almico switched from roasting on a fluid bed to a traditional gas fired drum roaster. Once he dialed in the roasts on both machines they tasted nearly indistinguishable in the cup.

I went from a Pro 100 to a Cormorant and have some initial impressions but need more time to come to an informed opinion on the matter.

In terms of cupping, the same profile (BT and ET)* gets the same taste; repeated blind cupping experiments have confirmed this. But there may differences in the bean surface that lead to differences in crema or pour over brewing behavior. Blind comparisons based on Immersion brewing would not show this.

* not as easy as it sounds, you need to manipulate the insulation and dose sizes to get the heat transfer just right -- our experiments were based on a PIDed P1 popper with custom roast chambers compared to both Quest and Hottop roasters, similarly instrumented, but manually controlled. We blinded the roasts and shipped them around for testing.

BTW, identical profiles on the bean temperature alone, with no reference to environmental temperature, were easy to tell apart. This means that claims about roasts based purely on BT (including ROR) should be treated with skepticism; they do not reflect all the variables affecting taste.

I think that the taste can be the same; the OP was talking about bloom. Watch Japanese language YouTube pourover videos and you'll see huge blooms that you'll never see in Western pourover videos (with coffees that look to have about the same colour). While most coffee in Japan is industrial like everywhere, pourover coffee shops typically roast their own coffee on 1kg or smaller roasters with no controlled airflow, e.g., http://www.youtube.com/watch?v=Vgu-EovJHDg , or roasters like the Fuji-Royal R-101's that have relatively little airflow (as far as I can tell). (There are also specialty shops using Lorings, etc. Videos from those shops look just like everywhere else)

For a while I was obsessed with Japanese Kissaten coffee, as demonstrated in the great 2014 documentary "A film about coffee" (you can watch the relevant bit in low-res here: https://www.facebook.com/watch/?v=191484748375691 ) or read about Daibo's shop here: https://roadsandkingdoms.com/2013/daibo/ (Daibo is the person roasting in the video in the first paragraph.) Over the years I've picked up all the equipment - a copper table-top roaster, a Fuji Royal R-440 shop grinder with the older (better?) version of their amazing ghost burrs, kettles and nel dripper, etc., but once I got my 'big' roaster that made nosebleed-light roasts easy, I went in that direction. However, I know that someday I will want to venture back into second crack ... and beyond .

My wife's dark roast coffee blooms like crazy, with small eruptions in the cup, gurgles, and cracks wide open. Takes 45 sec to settle down. Much different than our medium roast.

I am not noticing a difference in taste, just the bloom. Most of my roast average around 7-8 minutes on the Ikawa and around 10 min on the drum roaster.

I very well might be a conduction vs convection thing.