I have some very simple (I thought) goals:
1. Present two neighbouring 'H' glyphs with the stems closest to each other overlapping (and I don't care about next H(s))
2. Present two neighbouring 'L' glyphs with the heel of the right L just covering the toe of the left L (and I don't care about next L(s))
3. Present 'd' and 'P' with the stems closest to each other overlapping (and ...)

Common for all:
- basic Sans Serif
- the font will contain no other glyphs
- must correspond to latin characters/string (HH, LL, and dP) (not unicode 1000+)

I'm using FontForge, and I've tried to use kerning with no luck.
So far I've experienced the https://www.dafont.com/faq.php#nothing symptom, and tried all the suggestions in the FAQ.
- I have a GPOS lookup table of type 'Pair position (kerning)'
- with feature 'kern'
- subtable with the pairs and kern values (under the heading 'Δx #1', ~400 for HH and ~200 for LL)

Should this work?
What am I doing wrong?
Can I get the result I need in other ways?

In case you wonder, I could not be any greener with fonts, never worked with fonts until this week.
-AiwarikiaR