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I suggest setting the hero level and excluding the Diamond template.
Veteran is too easy, and Diamond is a very unpredictable template; it can generate castles that are two days' travel away. Also, there is a high risk of losing a Castle due to a random spawn from an opponent's portal.
And also, allow the Gnome to build a Tower – they are already rarely chosen, and this will at least make taking the Castle more challenging. The Tower isn't that scary, but the Gnome is slower.
Regarding the Diamond template, I agree; it's a questionable template, and in my active gaming practice, we practically don't play it. So, the suggestion is accepted, and I will discuss this with Primus today.
Added 6 minutes later
Regarding jumping... Sometimes, in the rules or by agreement, on templates where there is a Guardian (Spider-Labyrinth-Letos, for example), it is forbidden to jump into the starting zone until all Guardians have been defeated. This is open for discussion.
"Шанс есть всегда, но не везде." ;)