I think there are a number of ways to look at the question. If a shot isn't available on Micro and only RF on Alamy, then maybe it will sell there. I put my largest landscape panoramas on Alamy and never on Micro. In fact I try to put nothing on Micro that I have on Alamy. No similars, but one shot did get on both early on. It has sold on micro, never on Alamy.
Problem is, what people have pointed out. If someone is looking for price, they can find something else on SS that will fit their needs and unless you have the only image, that fits the need, if it's not on micro, it may just sit on Alamy.
I just don't feel like advertising myself on Alamy, competing with myself, so people can find the same shot for a buck on SS or a couple dollars on IS. Of course if the shot isn't up on Micro, it will never sell on micro!

I'd rather sell one shot on Alamy for $200 and get $120 than try to sell the same photo 480 times on SS. I don't know how many people keep track but my best selling image on SS hasn't sold 50 times yet. My best seller on IS has sold 17 times. So keep that in mind to understand why I prefer selling a shot once for $80-120 over Micro accumulated sales anywhere.
RM on Alamy, some selected large - possibly higher price RF on Alamy, smaller RF on Micro. Funny thing is, I don't bother, but a couple of shots that IS and SS rejected are now on Alamy RF. Rejected for lighting, but they were shot of the late in the day shadows and golden lighting. So much for Micro appreciating anything creative naturally. However if you grease paint someones face and stick feathers out their ears, have them stand next to a textured wall... now that's art to the micro reviewers.

What I'm getting at is, it depends. Some people may have shots that can work on both sites. I don't, and I'm not putting my editorial shots up for 25c on SS. IS doesn't take them. I don't shoot models and have one photo in three years with a model release. (which has never sold, by the way) Some isolations and lighting shots on Alamy have few views and no zooms. Similar to material that sells on Micro.
My Alamy sales bottom line, are greater than all micro agencies added together since I started. I'm not going to move my Alamy shots to Micro in hopes of making up the lost money with volume. That's the whole decision that people need to look at for their personal situation.
Can you make more volume on micro and earn more than holding out for those scattered big sales on Alamy? I can't with my images, others may find the opposite? Averaging $80 take home per download on Alamy. I'm not going to risk losing that for a bunch of small change Micro downloads of the same images. And where I started, I'm not going to compete with myself, selling a shot for Micro prices and on Alamy at the same time.
Last of all there's that integrity and price point argument, where I can't justify charging one person $200 for a shot, while I'm offering the identical photo as a subscription on SS or $8 download on IS. Would anyone reading this be pleased to buy a filter for their camera for $200 at a high end camera store and then find the identical brand, model and size, at a Dollar store in the shopping center. Be Honest! You would be angry and feel cheated.
That's why I don't sell the same images on Alamy and Micro.
