diff --git a/esphome/components/bluetooth_proxy/bluetooth_connection.cpp b/esphome/components/bluetooth_proxy/bluetooth_connection.cpp
index 37447e1ed9..4826b1dd38 100644
--- a/esphome/components/bluetooth_proxy/bluetooth_connection.cpp
+++ b/esphome/components/bluetooth_proxy/bluetooth_connection.cpp
@@ -17,7 +17,9 @@ static const char *const TAG = "bluetooth_proxy.connection";
 // The base UUID is stored in flash memory as constexpr
 static void fill_128bit_uuid_array(std::array<uint64_t, 2> &out, esp_bt_uuid_t uuid_source) {
   // Bluetooth base UUID: 00000000-0000-1000-8000-00805F9B34FB
-  // Pack 32/16-bit UUID directly into out[0] with bytes 12-15
+  // out[0] = bytes 8-15 (big-endian)
+  // - For 128-bit UUIDs: use bytes 8-15 as-is
+  // - For 16/32-bit UUIDs: insert into bytes 12-15, use 0x00001000 for bytes 8-11
   out[0] = uuid_source.len == ESP_UUID_LEN_128
                ? (((uint64_t) uuid_source.uuid.uuid128[15] << 56) | ((uint64_t) uuid_source.uuid.uuid128[14] << 48) |
                   ((uint64_t) uuid_source.uuid.uuid128[13] << 40) | ((uint64_t) uuid_source.uuid.uuid128[12] << 32) |
@@ -25,14 +27,16 @@ static void fill_128bit_uuid_array(std::array<uint64_t, 2> &out, esp_bt_uuid_t u
                   ((uint64_t) uuid_source.uuid.uuid128[9] << 8) | ((uint64_t) uuid_source.uuid.uuid128[8]))
                : (((uint64_t) (uuid_source.len == ESP_UUID_LEN_16 ? uuid_source.uuid.uuid16 : uuid_source.uuid.uuid32)
                    << 32) |
-                  0x00001000ULL);
-  // Pack bytes 0-7 into out[1] - this part is always the same for the base UUID
+                  0x00001000ULL);  // Base UUID bytes 8-11
+  // out[1] = bytes 0-7 (big-endian)
+  // - For 128-bit UUIDs: use bytes 0-7 as-is
+  // - For 16/32-bit UUIDs: use precalculated base UUID constant
   out[1] = uuid_source.len == ESP_UUID_LEN_128
                ? ((uint64_t) uuid_source.uuid.uuid128[7] << 56) | ((uint64_t) uuid_source.uuid.uuid128[6] << 48) |
                      ((uint64_t) uuid_source.uuid.uuid128[5] << 40) | ((uint64_t) uuid_source.uuid.uuid128[4] << 32) |
                      ((uint64_t) uuid_source.uuid.uuid128[3] << 24) | ((uint64_t) uuid_source.uuid.uuid128[2] << 16) |
                      ((uint64_t) uuid_source.uuid.uuid128[1] << 8) | ((uint64_t) uuid_source.uuid.uuid128[0])
-               : 0x800000805F9B34FBULL;  // Precalculated base UUID bytes 0-7
+               : 0x800000805F9B34FBULL;  // Base UUID bytes 0-7: 80-00-00-80-5F-9B-34-FB
 }
 
 // Helper to fill UUID in the appropriate format based on client support and UUID type