Some common fonts are equipped with countless anchors, up to 30 per glyph. Seems like every combining mark is positioned manually. While that certainly makes sense for high-end or general-purpose text fonts...
I've tried to minimize the number of anchors by having two exclusive sets of anchors for positioning above and below:
<div>[above] and [acute grave dotabove macronabove ...],</div><div><br></div><div>[below] and [ogonek cedilla dotbelow macronbelow ...].</div>
Each base glyph then either contains the single anchor or a full set of anchors from the other class, and each mark glyph contains the single anchor as well as one of the anchors in the extended set.
This way a big part of the base glyphs get away with just "above" and "below", and another big part with just one of the extended sets. I tested fonts produced with this approach and I didn't find any faults as long as the exclusivity of the anchor sets is preserved. I guess some validation tools might raise errors when a glyph doesn't contain all anchors? (or is it just the validator built into FontForge?). Do you know of any dangers with such approach?
Probably the commercial editors come with tools streamlining insertion of anchors, like inserting multiple anchors in the same spot or synchronizing anchor positions between glyphs, I wonder what is their output? For use with FontForge I developed a Python script copying mkmk anchors as mark anchors in derived glyphs, do the big editors do that automatically?
Btw: what about some more exotic anchors like comma-right-above? Do you think all base glyphs should contain one?