Begin with your anchor size
Your most-used kite should be chosen around local wind, rider weight, board and preferred riding style. The smaller and larger sizes should extend that useful range rather than merely follow a fixed numerical gap.
Keep the character coherent
A matched family gives predictable bar feel and handling across sizes. A mixed quiver can be better when one end has a specialist job, but the reason should be deliberate.
Price the complete setup
Kites, compatible control system and board should be considered together. A complete proposal also gives Kite Sports more room to create useful private package value than an isolated item does.