You're getting a little carried away...
If you start with a gravity above 1.18 or so (23% potential), the yeast will be unable to grow because there is so much sugar that it is toxic to them. This starts to be a problem even around 1.14-1.15, resulting in slow starts and off-flavors from stressed yeast.
I recommend starting at 1.10-1.11 with your first mead, which is 14-15 lbs of honey in five gallons. Unless you are diluting it half and half with fruit, don't worry about ABV dilution, or just add a bit (1/4 to 1/2 cup) of honey with the fruit to provide more fermentable sugars. There is also sugar in the fruit which will be fermented to alcohol, so the dilution will be 1-2 percentage points at most.
Also, using sugar is generally frowned upon, but if you only have 12 lbs of honey and want to make 5-6 gallons of mead, adding 2-3 lbs of sugar won't have a noticeable negative effect.
Concur with the "getting carried away" comment......
yeast doesn't just carry on making alcohol like some sort of factory. We happen to harness it's ability to make a certain amount.
Yet when you try to push the yeast too hard, you will likely stress it and get off flavours and other issues. Equally, the issue where the sugar levels make it impossible for the yeast to ferment is known as "osmotic shock" (it's why honey doesn't ferment unless we've watered it down a fair amount).
The
Lallemand yeast chart helps some. Yet, it's worth remembering that it will have likely been developed with grape musts etc. So should be used as a guide. We've already identified a few things that are worthy of note with it, in respect of honey musts - e.g. D47 needs to be fermented below 70F/21C otherwise it's been found that it produces fusels that take a long time, if ever, to mellow out. 71B-1122 is a good yeast for meads, especially fruit meads, but it's not suitable for "sur lie"/batonage ageing (ageing on the lees) as it's prone to produce "autolysis" off flavours if the ferment is left on the lees too long, etc etc.
The yeasts that boast the ability to go above about the 18 to 20 % mark are very specialist ones, and they need near perfect conditions to do that. Whereas it's easy to make brews of mead in the 12 to 16% area, yet the higher the strength, the longer they need to be aged to mellow out.
Equally, the other way, you can indeed, make low strength brews, but they then have similar problems to beer i.e. are drinkable quicker, but need near obsessive hygiene/sanitation as there's not enough alcohol to act as protection and preservative (10% ABV seems to be the minimum for that).
The high level alcohol you read of with some brews, invariably means that they're either fortified with spirits to increase the strength, like a "Port", or they're distilled to make a spirit - and that is a licensed practice anyway, hence not generally discussed hereabouts (plenty of distilling forums on the net to find out about that technique).
Just my tuppence worth........