func_pushable z-coordinate offset

I have 1 wierd question. Creating a func_pushable object respawn fix plugin I found out 1 wierd thing.

Coding part note:
We all know, that it's a brush entity, and we all know, that we can get its origin using this way (origin = mins+maxs). Then I asked myself - we valve made this **** insted of just using world coordinate (pev_origin)? And found out wery interesting thing - pev_origin is offset of all brush entityes. Anyway - using old method you just can get it's standart origin, but if you'll make +engine_origin, you will get the original position that is now.

But lets forget obout the coding for this moment. Anyway, my question is:
Are all func_pushable z-coordinate offsets are always +1.0? If you didn't understood what I have in mind sayng offset - look at clintmo_pentablock "func_pushable" objects - thay are all 1 unit higher. Can mapper change that 1 unit offset how he likes or dose engine teleports it 1 unit higher by standart?

why u need the pushable to be exactly on the ground ??
have u tried to lower the pushable with 1 unit to see if it works ??