This is not for a miata persay, at least for now, but was wondering if a small TMIC would be better than just pipe from the turbo to the IM? This is considering the pipe will be going over the engine.

 

As long as the intercooler is getting some sort of airflow then yes, anyone is better then none. If it sees no airflow it'll just become heatsoaked and be useless.

 

It is possible - at least on a very large engine with a very small intercooler - to get an IC so small its restriction outweighs its cooling benefits. Generally getting something that mismatched is a kind of badness you'd have to try to get there, like using a Saab sidemount intercooler on a twin turbo V8.

 

Yes, any intercooler is better than a hot pipe.

My little BEGi Cartech piece looked like it wasn't going to do much, but I saw pretty low IATs, never more than 20* above ambient. It was a front mount, but you can work out some ducting for a top mount.