Tivo HD upgrade (not XL)

Upgrade question about my Tivo HD (not an XL). I bought this used years ago. It had a 300GB drive installed (must have been upgraded by previous owner). I upgraded the 300GB to a 1TB drive, worked fine for years (did it myself using a boot CD, had to type in everything at prompts, MFS tools maybe?) Since the drive is getting old I decided to put in a 1.5TB drive. I read the Tivo HD will only support 1.2TB max. I used WinMFS to copy the 1TB onto the 1.5TB in it's entirety. When it finished it said I had extra space, did I want to allocate it. I assumed this meant it would allocate enough where I would have use of 1.2TB which I thought was the max. I said yes. Put the drive into my Tivo, it seems to have allocated the entire 1.5TB as my HD recording capacity went from 157 to like 230. Seems to be working so far but will I have problems in the future since I THOUGHT it could only use 1.2 TB (if I need to redo it how would I allocate it so I get only the 1.2, not the 1.5?) Thanks.