1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

for _ in range(int(input())):
    n = int(input())
    a = list(map(int,input().split()))
    n = max(a)
    k = 0
    for i in range(len(a)):
        if a[i]==n:
            if i==0:
                if a[i+1]<n:
                    k+=1
                    break
            elif i==len(a)-1:
                if a[i-1]<n:
                    k+=1
                    break
            else:
                if a[i+1]<n or a[i-1]<n:
                    k+=1
                    break

    if k!=0:
        print(i+1)
    else:
        print(-1)
