Currently (DF50/Arrow 56.1), DataFusion's support for the smaller decimals variants is limited. I've opted to not convert our decimal dtype into arrow's decimal32/64, even if the precision allows that. Once #4577 merges, we should keep an eye out on DataFusion, and once they release better decimal support we can enable the missing pieces on our end.

I have a PR in arrow-rs and another in DataFusion (with a second coming soon) that should enable that.

• Fix casting floats to Decimal64 apache/arrow-rs#8363
• Support Decimal32/64 types apache/datafusion#17501
• More decimal 32/64 support - type coercsion and misc gaps apache/datafusion#17808
• There will be another follow-up here that focuses on the DataFusion's SQL interface, but that shouldn't be a blocker for us.