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

l = int(input())
while(l):
    p = input()
    n = list(map(int,input().split()))
    m = max(n)
    if(len(set(n))==1):
        print("-1")
    else:   
        for i in range(len(n)):
            if(i==len(n)-1 and n[i]==m):
                if(n[i]>n[i-1]):
                    print(i+1)
                    break
            elif(i==0):
                if(n[i]>n[i+1] and n[i]==m):
                    print(i+1)
                    break
            
            elif(n[i]==m and (n[i+1]!=m or n[i-1]!=m)):
                print(i+1)
                break
            
        

    l-=1