The issue here is that value_template and position_template cannot been set concurrently in a template cover, so HA assumed the cover is open, when position is 100 and cover is closed when position is 0.
I found a “solution” which fits my needs, using two rows in an entities-card, except than just one. The first row uses the original entity, to control the cover with the buttons, the second row shows a slider and uses the template reverse entity, like the one you have:
- type: entities
entities:
- entity: cover.rollladen_arbeitszimmer
name: Rollladen
- entity: cover.revers_rolladen_arbeitszimmer
type: custom:slider-entity-row
full_row: true
hide_state: false
For the slider I use the custom slider-entity-row:
There is another custom card I use, which looks a bit different, but works for me too:
Maybe this helps you to find a solution, that fits your needs