Read this - Plenty of app point ideas:
But don’t get too hung-up on application. So long as it has a decent blood flow and is open to the air to diffuse, its viable. 
And if you are going for four days, be careful of build-up. A lot of these mones are the more sticky/long-lasting/persisting variety, or break down to them, so unless you find the time for a good bath/shower and scrub-up each day, you may find your dose being thrown-off by the remains of the previous day’s application. I’ve always found it good to reduce the primaries after the second day but the likes of IS snd P83 remain constant but other guys have adopted different strategies - again several threads if you search