Hi LH
I split my Lantus dose, I take my bigger dose first thing in the morning between 18 and 22, if my blood sugars are on the rise after tea and are above 13 at bed time I will another 8 units to gradually bring them down through the night.
If my sugars are on the lower side after teatime and up to bed time and I have done a lot of exercise that day, I will leave it . I think you are right in saying you will need to experiment.
Maybe have less carbs at lunch or try a couple more units of your fast acting at lunch if it is just an afternoon rise, but if it is a trend in your sugars that just keeps rising throughout the evening/night and you are high on a morning try taking a third of your morning Lantus dose and see how you get on with that.
I would set the alarm for in the night though for a few nights to make sure you are not going low.