Many russian aircraft had poor views from the cockpit, not only to the rear, but anywhere that you needed to look through glass. Ive heard from an VVS pilot, who sadly passed away not too long ago, that in his mig-1 he would get dizzy looking out the canopy because not all the glass was the same thickness and had the same visibility out of it, and wasnt mounted right, offering odd angles. I dont think the La series had it that bad, but that it was a problem to see the six.
The cooler was probably moved to the front because A.) it either simplified production or B.) It improved the aerodynamics.
Many soviet aircraft were rushed into production under horrible conditions and with shortages of every material, so aircarft were changed during production, because theyre were found unsuitable.