There could be a few variables involved with dosing when you switch from injections from infusion, and vice-versa. For instance, when I changed from 48 years of injections to a pump, I initially set pump settings to deliver only about 70% of the total [Lantus plus Humalog] insulin I was taking by injection.
A possibility for “spiking” could be that with a pump, your basal was covering a part of your mealtime bolus; have you considered changing your meal ratios? Remember, caution when making changes is imperative; you can always make a correction a few hours after eating.
As to depth of your injections, how does the length of the cannula you were using when pumping compare with the needle you are using? If the length is close, you can probably rule out that as your cause.
After a dozen years, faithfully rotating pump infusion sites between eight locations, I noticed I was getting absorption problems so I tried other body locations. Previously I had divided my abdomen into 8 areas and rotated between those areas; I then tried upper buttock and lower back areas which gave me problems then switched to upper arms. Now after giving my abdomen sections a year vacation I’ve returned there with wonderful results. Previously I had used 9mm cannula set at 90 degrees but now in my abdomen I’m using 17mm set at about 35 degrees. I did find that the 9mm were too long in my arms so I switched to 6mm for those locations.