DaveSSS 

I've followed bike geometry for over 30 years and have a binder full of old geometry charts. If you're familiar with the formula for calculating steering trail, you know that a given trail value can be achieved with different combinations of HTA and fork offset. It's common for larger frames to have steeper HTAs to avoid an overly long wheelbase and more slack on smaller frames to avoid excessive toe overlap and a too short wheelbase. Italians tend to use more trail than other builders. I like the larger trail that Colnago used for many years and I've owned four. Some brands offer frames with a small 58mm trail for all sizes. It's not right or wrong, but not what I want in a small frame.

My other point was that STA and HTA have no particular correlation, but smaller frames generally have steeper STAs and more slack HTAs, so it's common to have a HTA in the 71-72 range and a STA in the 74-75 range, so you shouldn't expect to see parallel angles. LOOK used to make frames with a 72.5 degree STA in all sizes.

Stack and reach now make getting the right frame size easier. If you know the stack that you want, find that first, then compare reach. The STA only affects your choice of seatpost setback. Right now, my Cinelli superstar has the saddle centered on a 25mm setback post, with a 74.5 degree STA. Some frames have proprietary posts and only one setback offering. My Yoeleo frames have a unique post that offers a wide range of setback at the seat rail clamp, with the maximum around 25mm. There are times when I have used 32mm setback seat posts.