Question about STACKING RULES

[Cole]

Fire Target Density Value: If the total SP in the target hex exceeds 12, 12 is then subtracted from that number to arrive at an Excess Density Value. This value is then multiplied by .08 (8%) and by the SP of the firing unit (fractions rounded up) resulting in a density bonus. This density bonus is added to the nominal SP of the firing unit.

Can't find anything in the rules but I'm almost 100% sure I've had units retreat into hexes with over 13 SPs. They don't retreat if it results in overstacking.

Don't forget that 6 SPs or more of wrecks in a hex block LOS along with 13 or more SPs of other units along with the over 12 SP penalty on a road hex (any unit moving that will bring the hex total over 12 SPs does not get the benefits of the road).