Granite stands for speakers experiment

there is a large Granite warehoue by me. I stopped by just to ask if they would sell me a small pieces. Turned out the owner is really cool and he let me pick some pieces from his "used" stock. He said he would only charge me a small fee for cuting ($25-$40).
So I picked 3inch slab and had them cut it to the size of the base of my ProAc D25 (10x11inch).

I placed my speakers on top of the 3inch granite blocks and of course the bass got better (ProAc woofer fires via bottom port), however the midrage got a bit bright.

I like how the low frequency improved but don't like what happened to the midrange.
Do you think if I was to use maybe 0.5inch blocks the midrange wouldn't be affected that way? I am guessing the cause is that the tweeters are now higher than they really should and it is not due to the material.

Anyone did that sort of experimentation? Maybe placing a little wooden blocks would be better?

PS: My room is carpeted.

Thanks!