I was going to suggest something similar.Another possibility is that Yokohama changed the tire, making it ride better, but handle less responsively. If that's the case, then your only recourse is changing the front tires to the new version.
How to determine that? Look at the DOT code. If the type code is different, it's likely the tires are different versions.
Type Code? I go into detail here: Barry's Tire Tech: DOT Codes
About 2/3 the way down, the third group of codes is explained. (There are 4 groups of codes.)
On Miata forum somebody experienced something similar. The tires were replaced in pairs, if I recall, and rear and front were made in different factories (different countries) - the same model, the same size.
The car handled "funny".
After replacing one pair to get single factory set of 4 the car returned to its previous balance.
Krzyś