read this...................
The Indian Army had two armoured regiments and three independent armoured squadrons supporting Lieutenant General Jagjit Singh Aurora's Eastern Command's thrust into East Pakistan. India had one T-55 tank regiment in the northern sector supporting the XXXIII Corps' offensive in the Hilli-Bogra area, with one PT-76 regiment in the western area supporting the II Corps' thrust. Finally three independent armoured squadrons (one PT-76, one AMX-13 and one Ferret armoured car) were supporting the IV Corps' offensive from the east. Opposing them were a Pakistani armoured force of a regiment of M-24 Chafees in the Bogra area, countering India's T-55 regiment and two squadrons of Chafeee tanks supporting the west and Dacca sectors.
When full scale hostilities began, half the tanks were either knocked out or captured by the time the Indian troops were on the outskirts of Dacca. After which the rest of the tanks were finally accounted for, as part of the surrender deal. In it's offensive, Indian losses were heavy. At least thirty PT-76 tanks were destroyed or damaged, another four T-55s had their tracks blown up over mines. The high loss rate among the PT-76 tanks was due to the fact that this type of tank had very thin armour plating to help assist its amphibious capabilities and was an easy target for mines. However all, but eleven, of the PT-76s were repaired after the war. The AMX-13s did not see much action and the Ferrets had no battle casualties.
so,as you can see,Even When in BD sector Pakistan had less armour(nearly all of them are light tanks),India deployed heavy tanks.in fact,your analysis is quite wrong.Bangladesh's terrain is quite ideal for tanks,except mountainous regions.Bangladesh is no more soggier than Indian West Bengal,which is in fact quite a friendly region.but yes,heavy tanks tends to less mobility in soggier regions.but BD is not that much soggier.
here,T-55 in BD
Various Pak Army Chaffee tanks captured after the Battle of Boyra on 21 November 1971