Placing the TECs on the top surface of the module introduces a few problems. The fans that will be needed to draw the considerable heat off the hot side of the TEC will have to dump that warm air outside of the case to avoid warming the inside of the projector and negating the advantage of the TEC. This cooling air turnover will bring potentially dirty air through your optical components. Secondly, the heat transfer from your diode depends on the cross sectional area of the heat conductor/the path length. Sending this heat to the edges of the module base, up the thinner walls and across the top of the module to the fans is a long and narrow road.