Experimental aircraft pilot reported while maneuvering in the practice area another aircraft was transitioning the practice area not transmitting on the UNICOM resulting in both aircraft taking evasive action to avoid a collision.

Narrative

Near miss with aircraft operating in a charted approved long term aerobatics practice area and a second aircraft on an instrument approach to runway XX at ZZZ. A NOTAM was published for aerobatic activities at the airport. The aerobatic airspace was activated with a call to ZZZ Approach at XA:15 (with aerobatics beginning at XB:45L) and a call was placed to deactivate the airspace at XC:11L. The aerobatic aircraft inadvertently exited the airspace 2 minutes late. The arriving instrument approach aircraft planned to arrive in the airspace at the end of the NOTAM. No inbound radio calls were heard by the aerobatic aircraft from the arriving instrument approach aircraft. Ground personnel monitoring the CTAF frequency (FBO) confirmed that no radio calls were received from the inbound instrument approach aircraft. Evasive action was taken by the instrument approach aircraft due to TCAS RA. Evasive action was taken by the aerobatic aircraft. No airborne communications occurred between the two aircraft. After action phone calls were initiated by the aerobatic aircraft pilot to instrument aircraft crew to acquire more information regarding the near miss. Potential causes: 1) Inadvertent late termination of aerobatics (2 minutes) by the aerobatic aircraft. 2) Lack of radio calls on CTAF by the instrument approach aircraft. 3) No notification by approach control to the instrument approach aircraft that the aerobatic airspace had not been deactivated. Preventative measures: Aerobatic pilot will recommend to have the Operating Terms of the FAA Certificate of Authorization of the Aerobatic Practice Area as follows:1. No aerobatics will commence until 10 minutes after the beginning effective NOTAM time and aerobatics will terminate 10 minutes before the end of the effective NOTAM time. 2. A ground safety observer on CTAF frequency will be in use at all times there are aerobatic activities below 2000' AGL. The ground safety observer will advise the aerobatic pilot of any aircraft that may be potentially entering the airspace without CTAF communications. 3. Activation / Deactivation airspace notifications to approach control will occur during the NOTAM window. (proposed change No. 1 will facilitate compliance)