They don't make it that easy to find the core info, but looking at the datasheet here -
https://www.alpha-batteries.co.uk/media/catalog/product/l/a/lagm-130.pdf - I would go for these settings:
Absorption Voltage - 14.4V (allowed range - 14.4V - 15V)
Float Voltage - 13.5V (allowed range - 13.5V - 13.8V)
Temp Coefficient - -20mV/Cel (recommended -30mV Charge, -20mV Standby)
If your 100/30 is the
SmartSolar model, you can set the exact parameters you want, so could set the above if you wanted. If you have the
BlueSolar only, then you are limited to the presets.
On the Presets above, the default setting (2) is the best match:
Absorption = 14.4V, Float = 13.8V. The temp coefficient is maybe a little more than you want though - 32mV/C, so in float mode you could be putting in too high a voltage at typical UK temps.