Not sure what the best lineup is against Miami; he's probably the best matchup on Ilgauskus (usually the backup). It is crucial that Sloan spreads the minutes around so that the team has the energy to play Orlando the next night. Utah is going to need Fesenko (or somebody) for a few minutes against Dwight Howard. Unfortunately, Sloan has not substantially raised Fes's minutes; he's still averaging less than 5 minutes per available game (although he might have been out for illness; I don't know if that's happenstance or his doing.)
Giving Al Jefferson (especially when he's struggled) 35+ minutes instead of 30 is not as valuable as giving the centers (combined) 20+ minutes instead of 10 or 15. So far, Elson and Fes have produced at about the same rate; but Fesenko has better assists, and he should be rewarded with more time. And if Sloan isn't gonna bench Jefferson for the abysmal boxing out repeatedly in the past two games, then he shouldn't bench Fesenko for offensive or defensive lapses either. Although Fes hasn't been perfect in help defense or boxing out, either, he has seems to have had more problem with still being too aggressive defensively rather than too lax.
Coaching 101.