V Belts

A small centre distance will imply a smaller arc of contact on the smaller pulley.

Reduced power transfer and slip.

Limited in the sense that the pulleys are touching?

The maximal distance between the pulleys is function of the own frequency of the belt working as a "cord" under tension. The higher the length the lower the frequency so that a resonnace could occur. The distance depends on the type (section), compound and inbeded es or fibers.

the main reason is heating due to the change from straight to curved as it goes around the pully. The smaller the radius = more heat = early failure

I assume this discussion applies only to "solid" V belts. Not to...what could I call it--"castellated" belts. Where the belt need not flex, only a small thickness of the outer diameter. Failure rate on these seems no worse, maybe better than solids on large pulleys...now 15 years with no apparent degradation and no loss of tension in my case.