Unless Iām mistaken, this is where the LFO Hold mode (if present on DN) would be best used, therefore no need to look at speed
If you can select a ramp shape (or Tri) LFO with the DN then try Hold with the ramp - and then vary the phase of the LFO so that you create an offset from zero (assuming phase is variable)
The LFO depth is then applied and spread across this smaller offset range - this at least works with other devices iirc and could allow finer control via depth and phase
Maybe DN doesnāt have hold mode, but the slow LFO with a phase/depth ramp should work out