Rich cruise in COS5

After enabling lean cruise mode on COS5 I have noticed a small issue. While I was doing a log I noticed that my commanded fuel afr was at 13:1 instead of 14.7:1. The only way I could get the commanded to follow B3647 was to drop speed down below the enable/disable speed. The reverse happens if the enabling happens in a low map area & an extremely lean condition can result. It seems that the pcm freezes whatever commanded afr is present in B3647 when the lean cruise criteria is met & then applies the correction until disabled.
Apart from time & coolant temp is there any other criteria that has to be met for lean cruise to be enabled? Can a map limit be applied to stop lean cruise applying when under an enriched cell area to prevent a rich cruise mode?