General rule is that contact is better matched with contact, and inert goes with inert (so creative+creative and leading+leading).

Contact and inert subtype have somewhat different needs in duality relationships, which only the same subtype can provide for them.

Contact subtypes start from a position of being hyperactive. As name implies, they make a lot of "contacts" with their environment. They need a partner is equally as responsive in a conversation and who will also stabilize them and calm them down. This is what happens when they meet their dual, whose contact functions fall directly on their own inert functions having a stabilizing effect and slowly filling their weakened inert functions which balances them out.

Inert subtypes start from a position of being inert and kind of sluggish/in their own head. They need is a partner who will 'speed them up' and incite them to come out and integrate information from their environment. This is what happens when they meet their dual of inert subtype whose hyperfocus on leading and activating functions begins to 'coax out' the creative and suggestive functions in them.

When contact and inert subtypes get together, this effect is lost. Mismatching creative/contact and inert/leading subtypes is thus not as complimentary and does not feel as fulfilling in relationships.

The contact/creative subtype may find their inert partner to be kind of boring and unresponsive, while the inert person might find the contact person to be irritating, talking without much substance to their words. There is also an overload on one set of information elements in these pairs, which creates disbalance in both shared info and on rationality-irrationality dichotomy, creating a sense of discomfort. For example I've heard SLI-Sis say that IEE-Fis are too 'pressuring' and 'exacting' for them, since between them there is a excess of rational element Fi. This eventually makes the SLI-Si want to slip away and distance. The SLI-Si needs an equally 'irrational' partner who appreciates same levels of freedom in a relationship, which they meet in the matching irrational subtype IEE-Ne.