As shown in this chart, the amount of over-carbonation of water with respect to air is less at higher pH (and lower TA) which is why the rate of rise in pH slows down as the pH gets higher especially when using borates since they buffer more strongly as the pH rises. Nevertheless, you usually see pH rise continuing when the TA is at 100 ppm -- you usually have to have it lower at 70 ppm or so for an SWCG. It all depends on the amount of aeration in your pool -- every pool is different. Just be thankful yours has become stable.