Coffee Appreciation

if there's loads of crema which goes quite dark on top but has disappeared by the time half has been drunk what needs to change?
pour time seems o.k 4-5 seconds start time after turning on then 18ish seconds.
new grinder (see above) and the dose is a bit lower so i have a good 5-6mm from top of tamped coffee to top of basket.

do i back off grind and up dose or just increase the dose and ease off the tamp (currently a fair bit of pressure)

beans are square mile winter espresso roasted on the 4th, classic/ascaso i-steel
previously been using shop ground (espresso room or monmouth) that always needs an overflowing basket and a hefty tamp as it's a bit too coarse but results have been good with lots of crema left up the sides of cup and smooth tasting.

That all sounds fairly normal, you're probably experiencing the effect of freshly ground coffee. 11 days post roast is about perfect for espresso, it will still have some co2 to release when you grind it which causes the crema to dissipate. Preground will have released all the gas by the time you use it which gives you a stable but very lacklustre crema. If you were to make espresso with beans roasted a day or 2 prior you would see loads and loads of rich dark crema dissipating within seconds. Doesn't mean it's not a good shot, it'll taste very young with lots of zingy rapidly changing aromas which jump around on the palate, as opposed to a nicely degassed rested coffee between 5 and 14 days post roast which will be more smooth, subtle and balanced. I enjoy both.