If your goal is to do a deep/high enema, then are a few tips I have learned from doing enemas for decades.
The first tip is to do a series of enemas which is at least 3 enemas. The first two are two-quart enemas. I will use either baking soda or epson salts- 2 tbs in a two qt enema. I use warm tap water not hot. The third enema will either be a 2 qt. or 3 qt. enema.
The first enema will be slow with some stop and starts with flow until I take the entire enema. So, the total hold time is at least 10 minutes or more from start to finish for the first enema. The second and third enemas will go a bit faster thus less in hold time.
And here is my best tip. I lay on my back on a yoga mat on the bathroom floor with the enema bag hanging from a towel rack about 4 feet above my anus. As the flow begins, I will raise my hips off the matt so the enema will now be draining down-hill into my colon. That gets the enema deep into the colon.
Another tip is to space the enemas maybe an hour or more apart. This allows the current enema to be expelled before you start the next one. This means each enema will have more room to fill your colon without competing with the previous enema.
Lasty, by the third enema, my expels have no solids and is a yellowish liquid. This is about as clean as I can get.
A word about nozzle types. I use a Silicone Nozzle butt plug nozzle which has a depth of about 5 inches. Now I do sometimes use a colon tube which can reach as far as 15 inches deep or more, but I would only use the colon tube on my third enema because now my colon is clear of solids. The colon tube will easily slide very deep with ease. The colon tube enables you to fill the colon very deep and this really gets you very clean.
My final word of advice is to practice frequently giving yourself enemas and pay attention to how your body reacts to the enemas. Be observant as to which little tricks work best for you to achieve your goals. If you enjoy enemas, you will enjoy the journey.